1. Field of the Invention
This invention relates generally to pool alarms, and more particularly to an improved swimming pool alarm that is sensitive to wave motion, but can discriminate between disturbances caused by entry of a small child or animal into the pool and those caused by wind, rain, etc. (false readings) via a comparator and timer system.
2. BRIEF DESCRIPTION OF THE PRIOR ART
Pool alarms have historically included a transducer placed below the water surface, which detects either high frequency sounds (acoustic) or low frequency disturbances (waves). In both types, an alarm is sounded when a threshold amplitude level is exceeded.
Acoustic pool alarms attempt to overcome the problem of excessive false alarms by sensing high frequency noise components. Although splashing sounds do have a high frequency component, so do loud noises such as traffic and hand clapping, as well as electromagnetic waves generated by nearby power lines. The potential for false alarms can be reduced by the inclusion of a filter, such as is found in U.S. Pat. No. 3,969,712, which filters out loud external noises and electrical disturbances by allowing only large high frequency components to pass through the filter, on to the detector.
Low frequency or wave sensor alarms to date have been found to be too sensitive, and small disturbances such as wind and rain will activate false alarms. If the sensitivity is reduced to a level that will prevent false alarms, the device may not detect the movement of a small child entering the pool. Additionally, these devices are made to float atop the pool surface, tethered by a string to the side of the pool. When someone wishes to use the pool, the device must first be removed from the water, untethered, and then put away to reduce the risk of damage to the device or injury to persons who might run into or trip over the device.